Specialty paper



SPECIALTY PAPER Filed Jan. 20, 1932 ZM' -f Ivy/6722277 w/#M ZMIZ??? film, A

mentes Feb. s, 193s Georgen.

Usmpalmlsrh,

samengaan-unserem Elkamcloflaine Application January i., 1982, Serial No, 587,180

This invention to papers which are intended forspeciaipurposesandwhichcantake.

the place of textile fabrics in suoli articles as towels, diapers,` L handkerchiefs, bandages. bed sheets. and the like. In all such connections. it is desirablethat the sheet be possessed of the proper resistance against disintegration when wetand atthesametimehavehighabsorbency and softness of feel. In accordance with the present invention, I prepare a sheet of unwoven fibers of interstitial and hence readily permeable structure whose interior layer or main body portion contains an agent existing as a continuous phase therein. importingy enhanced wet strength thereto but whose surface portions are much poorer in, or ysubstantiallydevoid of, such agents as compared with the interior layer or main body portion.

'I'he agent enhancing the wet-strength of the,

main body portion may be such adhesives as glue or casein, but' I-prefer to use. regenerated ce1- lulose derived from such cellulose derivatives as cellulose xanthate, cuprammonium cellulose, or the like, because of its high eifectiveness as a wet-strengthening agent. One of these agents maybeusedinsuchamoimtsstoenhancevastly the wet strength of the interiorvlayer of nbers,

- while at the same time substantially D its ultimate water-holding capacity. 1emm..

l Providing ses stance, through the'use of as little .as about 95% to 2% of regenerated cellulose. it is possible to eifect a multifold increase in the wet strength of the interior layer of fibers without significantly detracting from the original volume of voids or interstices therein i. e., the ready permeability of the layer to water. The wet-'strengthenms agents do, however, retard the rate at which water is imbibed by the interior layer. Moreover, thislayeritselfisstiilerandharsher'thanis desired in articles of the class mentioned.) By surface layers which are substantially A agent, these layers rptivity than the interior devoid ofwetare of quicker layer, bywhich I mean that they imbibe,

more quickLv than theainrior layer.

pscitythantheinteriorlayenwhichmaybeof adenserstructurethamforinstancatheordimrypper Ufsilbdlntlln! donotdependentirelyupontbsrats'ofabsorptivity or waterhoiding ,of the interinos* (ci. si-ss'i This meansthatl depend upon the surface layerstoactastemporaryspongesorreservoirs for taking up quickly and holding v'water and then transferring water to the interior layer,

which functions as a backing of high wet strength.' preventing disintegration of the composits sheet.

. With the foregoing and other features and objects in view, the present invention will now be described in greater -1 drawing, wherein 1 illustrates ventionally some of the g might be employed in preparing a sheet embodying the present invention.4

Figure 2 represents an enlarged sectionA through a sheet so prepared.,

In making a composite sheet embodying my invention, one may start with a bibulous waterleaf paper, that is, one which is substantially free fromsiaingornllingmateraiswhichdiminishitsabsorptivity. Yet the paper may be fabricated from papermaking stock which has been more or less beaten or hydrated to increase its so-called Mullen or bursting strength. The prefabricated paper web coming continuously from the dry end of the paper machine may be vely passed through, for instance, a bathv of viscose solution of a strength designed to carry away about to2% of cellulose in the form of xanthate into and throughout the web as a continuous pbase. The viscose solution may additionally contain boric acid, acetic acid. or other suitable agent in amount to promote the setting or regeneration of the cellulose as a continuous phase upon the drying of the web without, however, geiling thesolution so as t0 interfere with its penetrability. In Figure 1 of -thedrawing,1 have shown thepaper web 1 at the time when it is still wet with the wet-strengthdetail in conjunction with' imder the application of heat,

Ihewebsurfacesarestickyat.thissta8e.sothat superficiallayersoffiberscanbeanchoredthere-V to but without much influx of wet-strengthening agent into such-layers.v A pair of nozzles 2 are shownwiththeirdischitrlreencisfac-l the.web surfacesso asto deliver a current l carryingiiherunitsinsuspensionltherein` againstthesurfaces. Thefibersare preferably "sxtcrnaliayersbonthesurfacesoftheweba,

asillustratedinll'igure2. Anyiiberswhichdo thc-sticilywebsuriaces ening agent, say, in the form of viscose solution.

vthe maximum porosity and absorbency procurab ,on a paper machine, and so are eminently satisor do not become rmly'entangled with the anchored bers can be removed as by leading the resulting composite sheet between a pair of suction boxes 4 under sulcient suction to loosen and carryo such bers without, however, destroying the uify texture of the supercial layers as deposited. The sheet can then be heated to cause lthe setting of the wet-strengthening agent, which, in the case of viscose, is attained by the regeneration of cellulose as a continuous phase in the internal paper web. As depicted, the sheet may be passed over a bank of drier drums 5, through which steam is circulated as usual as the heating medium, whereupon the dried sheet can be accumulated as a roll 8.' 'Ihe sheet may be unwound from the roll 8 and formed into articles of the various kinds enumerated.

The bers used in forming the external layers may be of any suitable kind, e. g., chemical wood pulps, such as sulphite or kraft, pulps rened to high alpha cellulose content, cotton linters, mechanical wood pulp, etc. These bers may be used as such or in a mercerlned and/or mechanically powdered condition, together, if desired,- with more or less noncellulosic bers, such as wool, hair, and/or synthetic bers, su'ch as rayon. If desired, water-absorbent materials, e. g., hydrophilic colloids of the nature of soap and/or bentonite or other colloidal clays, may be admixed with the bers.

The principles of the present invention extend to composite sheets of the character described. which have been prepared from 'a paper web containing a suitable wet-strengthening agent as a continuous phase and from preformed layers or webs of paper of the requisite texture substantially devoid of wet-strengthening agent. The

latter webs may be of a loose, uify nature, prepared on papermaking machinery, which diifers from-the usual machinery in that little, if any, mechanical pressure has been applied to the webs during their. traverse of the wet and dry ends of the machine. 'I'his means that the webs I s factory'as the top or surface layers for the paper web containing the wet-strengthening agent. The latter web may be treated with a suitable adhesive applied as a continuous lm or onLv locally, to both its faces, whereupon the uy surfacing webs may be superposed and'the adhesive caused to dry or set and thereby bond the plies into a unitary sheet. When the interior ply is still wet with the wet-strengthening agent, e. g., viscose solution, that present on the surface can be relied upon for bonding the superposed plies thereto.

wIn those instances when the surface layers of the sheet are formed directly on the paper web containing the wet-strengthening agent, it may be desirable to start with a the wet-strengthening agent has already been dried or set. For instance, it may be desirable to start with a dry paper web containing regenerated cellulose distributed therethrough as a conpaper web in whichv tinuous phase enhancing the-wet strength of the web. In such case, it is necessary to condition the web for receiving and anchollns the loose, individual ber units sprinkled thereonto. and thereby acquiring an attached layer g the desired qualities of absorbency and softness. To this end, the dry paper web containing the wetstrengthening agent may be rewet with an aqueous solution of the same agent but in such dilution that even if it enters into the supercial deposits lof ber, they will contain much less of such agent than the internal paper web. Thus, a dried paper web-containing regenerated cellulose may be a solution may beA sprayed or otherwise applied to the bers being deposited on the web, so that these bers cling to=the dry web and\then become permanently xed thereto as a layer upon subsequent drying. The solution, e. g., viscose, sprayedonto the bers should be of such low strength as to be' compatible with the formation of applied exterior ber layers of the desired qualities.

What I claim is:

l. A composite sheet comprising a porous, readily permeable and absorptive paper base containing a wet-strengthening agent selected from a class consisting of glue, casein, and regenerated cellulose, said agent being distributed therethrough in amount occupying only a small fraction of its pores but enhancing vastly its wet strength, and a uy layer of cellulose ber attached to at least one surface of said paper base and being 'of greater absorptivity but much lower wet strength than said paper base, said uiiy layeretaking up quickly and holding water and transferring such water to the paperbase and said readily permeable paper base serving as a backing of high wet strength and preventing the disintegrationoi the composite sheet.

2. A composite sheet comprising a porous readily permeable and absorptive paper base containing regenerated cellulose distributed therethrough in amount occupying only a small fraction of its pores but enhancing vastly its wet strength, and a uffy layer of cellulose ber attached to at least one surface of said paper base and being of greater absorptivity but much lower wet strength than said paper base, said uy layer taking up quickly and holding water and transferring such water to' the readily permeable paper base and said paper base serving as a backing'of high wet strength and preventing the disintegration of the composite sheet.

GEORGE A. RICHTER. 

